chapter 5 EXAM 3 Flashcards
radiation survey instruments
area monitoring devices that direct and measure radiation
personnel dosimetry
the monitoring of radiation exposure to any person occupationally exposed on a regular basis to ionizing radiation
exposure monitoring is required when radiation workers are likely to receive
10% or more of the annual ocupational EfD limit in any single year due to their work activity
most healthcare facilities issue dosimeters when personnel could receive
1% of the annual occupational EfD limit in any month
what is the purpose of personnel dosimeter
for your safety.
determines the amt. of exposure by measuring the amt. of ionizing radiation the dosimeter has been exposed to
detects and measures the amt. of radiation it has been exposed to
placement of personnel dosimeter
during routine radiographic procedures
attached to the clothing on the front of body at collar level to approximate the dose to thyroid, head and neck
placement of personnel dosimeter
when a protective apron is worn
outside apron at collar level in the front
placement of personnel dosimeter
as a second monitor when a protective apron is worn
1st dosimeter worn at collar level
2nd dosimeter worn beneath apron at waist level (measures dose to lower body trunk)
commercial lead aprons have how much lead equivalent
0.5 mm lead equivalent over all
commercial lead aprons have how much lead equivalent in a less heavy version
0.35mm lead in the front and 0.25mm lead in the back
monitor for the embryo-fetus
wears primary dosimeter at collar level
second monitor records dose to the abdomen worn at waist level
extremity dosimeter
used when performing fluoroscopic procedures when hand is near primary beam
measures dose to hands of the wearer
extremity dosimeter contains the following info
account number, name, wear date, R or L hand, size and reference number
TLD stands for
thermoluminescent dosimeter
characteristics of personnel dosimeters
lightweight/easy to carry
durable
able to detect large and small exposures
outside influences should not affect its performance
inexpensive
4 types of personnel dosimeters
- optically stimulated luminescense (OSL)
- film badges
- thermoluminescent dosimeter (TLD)
- pocket ionization chambers
when were optically stimulated luminescense dosimeters developed
the late 1990’s
optically stimulated luminescense (OSL)
most common type
are replacing film badges
a combo of film and TLD while eliminating their disadvantages
OSL dosimeter contains
an aluminum oxide detector
and is read by a laser light
the OSL dosimeter can be worn for
1 year but commonly is switched out every 1-3 months
what is the inhouse reader called that landauer does sell
microStar
this allows occupational exposure to be read the day of occurrence
what are the 3 different filters in an OSL badge
- copper
- aluminum
- tin
T or F
aluminum absorbs the least in an OSL badge
true
T or F
copper attenuates the most in an OSL badge
true
when high energy radiation strikes the OSL dosimeter,
the laser reading would show a similar reading through all the filters
when low energy radiation strikes the OSL dosimeter,
the laser reading would be more pronounced in the region covered by the aluminum filter
T or F
OSL dosimeters are extemely sensitive
true
the increased sensitivity makes it ideal for monitoring employees working in low radiation environments
control monitor
the monitoring company provides this with each batch of dosimeters to make sure when they are transferred the reading is not compromised by anything that comes from the outside environment.
advantages of OSL monitors
lightweight, durable color coded tamperproof extended wear frequencies increased sensitivity inexpensive
an OSL dosimeter has an accurate reading as low as
1 mrem (10microseiverts) for xray and gamma ray photons with energies ranging from 5KeV to greater than 40 MeV
disadvantages of OSL monitors
exposure is recorded only in body area where it was worn
exposure cannot be determined on day of exposure
must wear it for it to be efficient
Film Badge consists of
film holder
metal filters
film packet
when did film badges come into use
1940’s
film holder
made of plastic
has low atomic number
metal filters
located inside film holder
made of aluminum and copper
allow measurement of approximate energy of radiation
determine direction it reached film
determines if exposure was from scatter or primary radiation
film packet
sensitive to doses ranging from 0.1 mSv to 5000mSv
doses below this are not usually detected and reported as minimal
lead foil on back of film to absorb scatter coming from behind dosimeter
radiation interacting with film badge causes the film to
blacken
function of control badge
serves as a basis for comparison
increased optical density on a film badge is read with
a densitometer
personnel monitoring reports
accurately records and maintains records to meet state and federal regulations
supplies written personnel report to health care facility
change in employment by radiation worker
must convey the data pertinent to accumulated equivalent dose to the new employer to be placed on file
advantages of film badges
permanent legal record of personnel exposure
economical
mechanical integrity
disadvantages of film badges
temp and humidity can cause fogging
exposure cannot be determined on day of exposure
less sensitive to ionizing radiation
thermoluminescent dosimeter (TLD) detector is made of
sensing material is lithium flouride
how TLD dosimeter works
radiation causes electrons in the lithium flouride molecules to absorb energy and become excited to higher energy levels and become trapped.
after being passed through special heating process trapped electrons return to normal state and emit light
TLD analyzer measures
the amount of ionizing radiation by heating crystals to free trapped electrons and records amount of light emitted
advantages of TLD
interacts with ionizing radiation as human tissue does
exposures as low as 1.3x10^-6c/kg can be measured precisely
environmental factors do not affect it
may be worn up to 3 months
crystals can be reused
disadvantages of TLD
high initial cost
readout process destroys stored info
pocket ionization chamber
most sensitive type of personnel dosimeter
use in diagnostic imaging is uncommon
looks like a pen
2 types of pocket ionization chambers
- self reading type (built in electrometer)
2. non self reading type
components of pocket ionization chamber
contains 2 electrodes one positive one negative
when charged electrodes are exposed to xrays or gamma rays the positive electrode becomes ionized and discharges mechanism in proportion to amount of radiation to which it has been exposed
t or f
you need a special charging unit for a pocket ionization chamber
true
pocket ionization chambers are sensitive to exposures ranging from
0 to 5.2x10^-5 c/kg
advantages of pocket ionization chamber
immediate readout compact convenient accurate and sensitive ideal for short duration
disadvantages of pocket ionization chamber
expensive
must be read each day
subject to mechanical shock
could get false reading if dropped
3 types of radiation survey instruments for area monitoring
- ionization chamber-type survey meter (cutie pie)
- geiger muller detector (GM) (seen in nuc med)
- proportional counter
requirements for radiation survey instruments for area monitoring
portable durable reliable interact with ionizing radiation similar to human tissue detect all common types of radiation cost effective calibrated annually
ionization chamber-type survey meter
CUTIE PIE
small in size
measures exposure rate (c/kg)
used for area surveys
measures x and gamma radiation
sensitivity range of the CUTIE PIE
measures intensities from 1 mR to several R
advantage of the cutie pie
able to measure a wide range of radiation exposure within a few seconds
disadvantages of the cutie pie
delicate
without adequate warm up reading may be inaccurate
cannot measure diagnostic procedures because exposure times are too short
what is the cutie pie most commonly used to measure
exposure rates at various distances from patient who has received radioactive material for diagnostic or therapeutic use
proportional counter
serves no purpose in diagnostic imaging
used in alb setting to detect alpha and beta radiation
geiger muller detector
primary portable radiation survey instrument for area monitoring in nuclear medicine facilities
detects area contaminated by radioactive material
locates lost radioactive source or low level radioactive contamination
geiger muller detector components
has an audible sound system that alerts operator to the presence of ionizing radiation
disadvantages of the geiger muller detector
not independent of energy of incident photon
saturates or jams when placed in very high intensity radiation area giving a false reading
